Silver Lake prepares for the big bore

A tunnel boring machine of the type that maybe used in Silver Lake. Photo courtesy LADWP

The streets of Silver Lake have been torn up, motorists have faced ongoing detours and residents have worried about their health in the wake of construction noise and dust. All this is the result of the installation of large new water pipelines that are part of an L.A. Department of Water & Power project to bypass and take the Silver Lake and Ivanhoe reservoirs out of commission in order to meet more stringent federal water guidelines. The detours, dust and noise are far from over as DWP crews work to tear up more streets and lay new pipe. But, early next year, part of the construction will be out of sight with the arrival of a giant boring machine that will dig out a nearly mile-long tunnel under the homes and streets west of the Silver Lake Reservoir. Earlier this month, Glenn Singley, Director of Water Engineering for the DWP, updated residents on what’s called the Silver Lake Bypass Tunnel, which will begin at West Silver Lake Drive just south of Balmer Drive, run underneath Redesdale Avenue and then emerge near the Silver Lake Recreation Center.

The tunnel boring machine will work from north to south, digging out about 38 feet of dirt a day as crews remove trucks loads of dirt and install rings of steel and concrete in the newly carved out tunnel. Part of the this project will mean shifting a section of West Silver Lake Drive and the reservoir walking path to the east to build an approximately 40-foot wide “launch pit” where the tunnel machine will be dropped into place. Also, on the far north side of the Ivanhoe Reservoir near Armstrong Avenue, a grassy area near Armstrong Avenue on the north side of the reservoir as a staging and storage area for the tunneling project. The DWP provided more details about Silver Lake’s Big Bore in a Q & A below.

Why build a tunnel in this section instead of a trench along Silver Lake Boulevard?
A cost study performed by LADWP revealed that tunneling was the most cost effective method of installation for the proposed pipeline. The depth requirements of the proposed water pipeline would require extensive shoring methods and continuous dewatering operations due to the high groundwater table, making the open trench method more costly than the tunneling option.

How wide would this tunnel be?
The tunnel will have a minimum diameter of 10 feet. It will be made of welded steel pipe lined with precast concrete rings for support.

Would the tunnel simply serve as a pipe for water or will it contain other things?
The pipe will convey water, nothing else.

How long is the tunnel? How deep will it go?
The tunnel will be approximately 4,600 feet in length at a depth ranging from 60 to 145 feet.

How much earth will have to be excavated and trucked out?
Approximately 22,000 cubic yards of soil will be excavated and removed.

What kind of machine and crews will be used for the tunnel? Will it run all day? How many feet a day will be drilled out?
A tunnel boring machine (TBM) will be utilized for this tunneling operation. The crew will consist of personnel with specialized skill in tunneling operations. The daily operation will run during a 10-hour work shift. Current production rates for this project are estimated at 38 feet per day.

How long will it take to complete the tunneling project?
The tunneling operation is estimated to be completed within 26 months.